I. Field of the Invention
The present invention relates generally to the field of receiving and recording signals indicative of or inducing cardiac activity (mapping) and transmitting electric energy or radio frequency (RF) power to tissue surfaces (ablating) using steerable vascular cardiac catheters. The invention is particularly directed to a mapping and ablation catheter electrode system which can precisely locate localized cardiac electrical activity signals regardless of the direction of the propagation wavefront and yet create linear continuous lesions of significant size.
II. Discussion of the Related Art
Steerable catheter systems of several types have been devised. Such devices can be inserted into blood vessels or similar bodily areas and their distal ends navigated through the tortuous vascular path to reach areas of the body normally inaccessible without surgery. Catheters of the steerable or self-navigating type, having distal electroded sections for monitoring parts of the body, such as for electrically mapping the heart by receiving and transmitting electrical signals related to the operation of that organ to recording signal processing and display devices are also known. The ability to successfully record impulses or signals and from them electrically map the cardiac chambers and valves using flexible catheters having steerable electroded tips has further led to the use of the technique of transcatheter ablation of cardiac tissues that have been identified as the cause of cardiac arrhythmias. This technique has emerged as one of the most important advances in cardiac electrophysiology. Its goal is to destroy the arrhythmogenic tissue without compromising the mechanical or muscular integrity of the cardiac tissues and vessels.
Not long ago, for example, many patients with Wolff-Parkinson-White syndrome or ventricular tachycardia underwent surgical dissection of the arrhythmogenic tissue followed by a painful and prolonged recovery. Introduction of the transcatheter approach has dramatically reduced the suffering and cost of this definitive treatment for many causes of cardiac arrhythmias.
The general approach to this procedure initially preferably utilized high energy direct current delivered to the catheter poles, for example, to disrupt the A-V node condition and even to create a complete heart block by ablating the His bundle. The diffuse nature of direct current energy tissue injury, the relatively high rate of serious complications and the limited ability of the operator to control the energy delivered have limited the usefulness of this approach and have led to the development of approaches using alternative energy sources. As a result, more recently, radio frequency (RF) has replaced high energy direct current as the preferred primary source of energy and the transcatheter approach for cardiac ablation has become an accepted and common procedure and has been used increasingly as the primary mode of treating cardiac arrhythmias. Transcatheter cardiac tissue ablation is more fully discussed in Avitall et al, "Physics and Engineering of Transcatheter Tissue Ablation", JACC Volume 22, No. 3:921-32. The rapid clinical acceptance of this procedure and the proliferation of physicians engaged in transcatheter tissue ablation has mandated the development of improved steerable catheter devices with more sophisticated electrode configurations.
In order to produce large, rather deep lesions to ablate certain arrhythmias, particularly those associated with ventricular tachycardia due to reentry in patients with a history of heart attacks, or to produce longer linear lesions, the trend has been to employ longer or very large distal tip electrodes requiring rather high RF power for use with RF ablation. Electrodes up to 12 mm long are described by Langberg et al, for example, "Temperature-Guided Radio Frequency Catheter Ablation with Very Large Distal Electrodes" in Circulation, Vol. 88, No 1, Jul. 1993 (pp. 245-249). This approach is typical of the current trend. While such large electrodes are useful for increasing lesion size and ablating tissue, this is not achieved without compromising the ability to discretely map localized electrical activity. Thus, there remains a definite need for the provision of an electrode system which not only enables the production of any desired size lesion, but also enables the operator to maintain accurate localized mapping ability using the same electrodes.
Accordingly, it is a primary object of the present invention to provide an improved mapping/ablation electrode arrangement which provides for flexible lesion size yet maintains discrete localized mapping ability.
Another object of the present invention is the provision of a segmented ablation/mapping multi-electrode system that maintains the ability to map localized electrical activity irrespective of directionality of the propagating wavefront.
Yet another object of the invention is the provision of a segmented or multi-electrode mapping/ablation system that enables the operator to adjust the lesion size (width, length and depth).
Other objects and advantages of the invention will occur to those skilled in the art in accordance with the following description, specification and drawings.